1. Field of the Invention
This invention relates to digital solid state logic circuits which utilize a single power supply, employ Schottky diodes as the logic elements and use logic signals to the control current in an E-mode FET.
2. Related Art
Eden introduced Schottky diode field effect transistor logic (SDFL) in U.S. Pat. No. 4,300,064. Therein Schottky diodes are used as logic switching elements and the logic signal is used to switch a depletion mode field effect transistor (D-FET). A negative power supply is connected to the cathodes of the Schottky diodes (via a voltage level shifting diode) and to the gate of the switching D-FET. The negative power supply provides the negative potential necessary to switch the negative threshold D-FET. A positive power supply supplies current to the drain of the switching FET via a gate-source shorted D-FET.
Eden's use of Schottky diodes as logic elements reduces the size of logic circuits relative to those employing only FETs as the nonlinear switching elements, and provides a fast switching circuit.
In U.S. Pat. No. 4,405,870 Eden expanded on the above patent by connecting several AND branches in parallel. He labeled this expanded version Schottky diode-diode FET logic (SD.sup.2 FL). Each AND branch includes a plurality of Schottky diodes as the nonlinear switching elements. The anodes of the switching Schottky diodes are all connected in parallel at a common node. A first pull-up current source is connected to the common node, as well as a negative source of potential (via a series of voltage level shifting diodes). The shifted voltage is used to drive a switching D-FET. The drain of the switching D-FET is connected to a positive source of potential via a source-gate shorted D-FET (i.e. a second pull-up current source). The output is taken at the drain of the switching D-FET. The source of the switching D-FET is grounded.
The above circuits are compact and fast, but the requirement of positive and negative power supplies increases circuit complexity.